Simple Question about Resultant Force and Direction in Statics

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In summary, the question involves using the law of cosines to find the resultant force, which is 139.1 lb. However, there is confusion about the direction of the force, with the textbook stating 67 degrees while the calculation gives 113.1 degrees. After some discussion, it is determined that the correct direction is 67 degrees, which may be due to rounding and the graphical method used to solve the problem.
  • #1
68
4

Homework Statement


http://img11.imageshack.us/f/screenshot20110117at120.png/

The question is 2.3


Homework Equations


Law of cosines and law of sines.


The Attempt at a Solution



I used the law of cosines to find the resultant force. It is 139.1 lb. However, I get 113.1 degree for the direction of the resultant force. The textbook says that it is 67 degrees. I noticed that I get 67 degrees if I subtract 139.1 from 180 degrees. Why is this? Also, I am a little confused about significant figures. Why are they giving only two sig figs for the direction?

Thanks
 
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  • #2
Marioqwe: Usually you give the vector direction measured from a horizontal axis. Try that. They might be listing only two significant digits because the question asks you to determine the answer graphically, which is a less precise method than a calculator. Anyway, the correct answer is 67.0 deg, which rounds to the same answer.
 
  • #3
Thank You for your reply. It is more clear now.
 

1. What is the definition of statics?

Statics is a branch of mechanics that deals with the study of objects at rest or in a state of constant motion.

2. What are the main principles of statics?

The main principles of statics include the equilibrium of forces, the concept of moment, and the properties of distributed loads.

3. How is statics different from dynamics?

Statics deals with objects at rest or in a state of constant motion, while dynamics deals with objects in motion and the forces that cause that motion.

4. What are some real-life applications of statics?

Statics is used in the design and analysis of structures such as bridges, buildings, and machines. It is also used in the study of fluid mechanics and in the field of biomechanics.

5. What are some common tools used in statics?

Some common tools used in statics include free body diagrams, equations of equilibrium, and vector mathematics. Computer software such as finite element analysis is also commonly used in more complex applications.

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